Techniques for improving adhesion of silicon dioxide to titanium

ABSTRACT

The present invention is described in several embodiments depicting structures and methods to form these structures. A first embodiment is a structure having a silicon dioxide film bonded to a metal film comprising: a metal nitride film bonded to the metal film; and the silicon dioxide film bonded to the metal nitride film. A second embodiment is a structure having a silicon dioxide film bonded to a metal film comprising: a metal oxide film bonded to the metal film; and the silicon dioxide film bonded to the metal oxide film. A third embodiment is a structure having a silicon dioxide film is bonded to a metal film comprising: a metal/oxide/nitride film bonded to the metal film; and the silicon dioxide film bonded to the metal/oxide/nitride film.

This is a continuation to U.S. patent application Ser. No. 09/645,958,filed Aug. 24, 2000 now U.S. Pat. No. 6,365,530, which is a divisionalto U.S. patent application Ser. No. 08/744,298, filed Nov. 06, 1996, nowU.S. Pat. No. 6,144,098, which is a continuation to Ser. No. 08/228/054now U.S. Pat. No. 5,624,868, filed Apr. 15, 1994.

FIELD OF THE INVENTION

This invention relates to a semiconductor structure and fabricationprocess and more particularly to techniques for forming a structure thatprovides adhesion between silicon dioxide and titanium.

BACKGROUND OF THE INVENTION

During semiconductor fabrication it is common to use silicon dioxide(SiO₂) as an insulator between metal layers due to its superiordielectric properties. It is typical to form atitanium/aluminum/titanium (Ti/Al/Ti) stack for use as a metal1 layer.Over this metaI1 stack a thick film of plasma SiO₂ is deposited. Usuallybefore a metal2 layer is deposited on the dielectric, topographyvariations existing on the dielectric are smoothed out by planarizationtechniques such as chemical-mechanical polishing (CMP).

Unfortunately, the polishing technique by its very nature induces a lotof stress at the interface between the metal1 layer and the dielectriclayer. Extensive peeling of the dielectric is observed if the adhesionbetween the metal and dielectric is poor, which is highly undesirable.

The present invention addresses the poor adhesion that can exist betweena metal layer and a dielectric layer in the several embodimentsdescribed hereinafter.

SUMMARY OF THE INVENTION

A first embodiment of the present invention is a structure having asilicon dioxide film bonded to a metal film comprising:

a metal nitride film bonded to the metal film; and the silicon dioxidefilm bonded to said metal nitride film.

The structure of the first embodiment is formed by a semiconductorfabrication process for adhering silicon dioxide to metal comprising thesteps of:

cleaning the surface of the metal;

converting the cleaned metal surface to a metal nitride; and

forming silicon dioxide subjacent to the metal nitride.

A second embodiment of the present invention is a structure having asilicon dioxide film bonded to a metal film comprising:

a metal oxide film bonded to the metal film; and

the silicon dioxide film bonded to the metal oxide film.

The structure of the second embodiment is formed by a semiconductorfabrication process for adhering silicon dioxide to metal comprising thesteps of:

cleaning the surface of the metal;

forming an oxygen deficient film on the metal surface; and

forming a silicon dioxide layer over the oxygen deficient film, therebycausing a chemical reaction between the oxygen deficient film and themetal to form an interfacial metal oxide bonding layer therebetween.

A third embodiment of the present invention is a structure having asilicon dioxide film bonded to a metal film comprising:

a metal/oxide/nitride film bonded to the metal film; and

the silicon dioxide film bonded to the metal/oxide/nitride film.

The structure of the third embodiment is formed by a semiconductorfabrication process for adhering silicon dioxide to metal comprising thesteps of:

cleaning the surface of the metal;

converting the cleaned metal surface to a metal nitride;

forming an oxygen deficient film on the nitrided metal surface; and

forming a silicon dioxide layer over the oxygen deficient film, therebycausing a chemical reaction between the oxygen deficient film, the metalnitride and the metal to form an interfacial metal/oxide/nitride bondinglayer therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a represents a process flow diagram of the first embodiment;

FIGS. 1b-1 d represent composite cross-sectional views of an in-processsubstrate portion depicting the resulting structure following theprocess flow of FIG. 1a;

FIG. 2a represents a process flow diagram of the second embodiment;

FIGS. 2b-2 d represent composite cross-sectional views of an in-processsubstrate portion depicting the resulting structure following theprocess flow of FIG. 2a;

FIG. 3a represents a process flow diagram of the third embodiment, and

FIGS. 3b-3 e represent composite cross-sectional views of an in-processsubstrate portion depicting tie resulting structure following theprocess flow of FIG. 3a.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the present invention is depicted in FIGS. 1a-1 d.a second embodiment of the present invention is depicted in FIGS. 2a-2d, and a third embodiment of the present invention is depicted in FIGS.3a-3 e.

In a first embodiment and referring now to FIG. 1a, the generalprocessing flow is outlined. First the surface of a metal is cleaned (asrepresented by box 1) by such methods as subjecting the metal to anargon plasma. When subjecting the metal to argon plasma, the desiredresult is accomplished by performing a sputter clean at a pressure ofapproximately 30 mTorr, at an energy of approximately 200 W RF power, atan argon flow rate of approximately 50 sccm and for a time period ofapproximately 10 sec. Even better results are obtained when employing amagnetic field of approximately 60 Gauss during the sputter clean.However, the range for each of the parameters can vary. For example, thesputter clean can be performed at a pressure range of 10-50 mTorr, at anenergy range of 100-500 W RF power, at an argon flow of 20-70 sccm andfor a time period of 5-50 sec.

Next, the metal surface is converted to nitride (as represented by box2) by such methods as subjecting the cleaned metal surface to plasmanitridation comprising N₂+NH₃ plasma. When subjecting the metal surfaceto plasma nitridation, the metal surface is placed in an N₂/NH₃ ambientfor approximately 15 sec, at a pressure of approximately 4.5 Torr, at atemperature of approximately 360° C. and at an energy of approximately350 W RF power. It is preferred that the N₂:NH₃ ratio is 10:1, howeverit is sufficient if the ratio ranges from 2:1 to 50:1.

Finally an SiO₂ layer is formed on the metal nitride (represented by box3) by methods known to those skilled in the art.

A specific example resulting from the process steps of FIG. 1a isdepicted in FIGS. 1b-1 d. Referring now to FIG. 1b, a metal stackcomprising Ti layer 11, Al/Cu layer 12 and Ti layer 13 has been formedon a supporting substrate 10 (supporting layer 10 represents anymaterial used in a fabrication process that the metal stack can beformed upon). Ti layer 13 is then cleaned by a method such as the onedescribed for FIG. 1a.

Referring now to FIG. 1c, the cleaned surface of Ti layer 13 is exposedto plasma nitridation by a method such as the one described for FIG. 1a.The resulting nitridation of the surface of Ti layer 13 forms TiN layer14. As FIG. 1c shows, though a portion of the Ti is converted to TiNlayer 14, a non-converted portion of the Ti remains as depicted by theremaining Ti layer 13.

Referring now to FIG. 1d, an SiO₂ layer 15 is formed on the TiN layer 14by methods known to those skilled in the art. TiN layer 14 is the layerthat adheres SiO₂ layer 15 to Ti layer 13.

In a second embodiment and referring now to FIG. 2a, the generalprocessing flow is outlined. First the surface of a metal is cleaned (asrepresented by box 1) by such methods as subjecting the metal to anargon plasma. When subjecting the metal to argon plasma, the desiredresult is accomplished by a performing a sputter clean at a pressure ofapproximately 30 mTorr, at an energy of approximately 200 W RF power, atan argon flow rate of approximately 50 sccm and at a time period ofapproximately 10 sec. Even better results are obtained when employing amagnetic field of approximately 60 Gauss during the sputter clean.However, the range for each of the parameters can vary. For example, thesputter clean can be performed 15 at a pressure range of 10-50 mTorr, atan energy range of 100-500 W RF power, at an argon flow of 20-70 sccmand for a time period of 5-50 sec.

Next an oxygen deficient film is formed on the metal surface asrepresented in box 4. For example, the oxygen deficient film comprisesSiO_(x) that is formed by the plasma dissociation of tetraethylorthosilicate (TEOS) where x varies from 1-2 (x is less than 2 to beclassified as oxygen deficient, or in this embodiment, x ranges from 1to less than 2).

Finally, an SiO₂ film is formed over the oxygen deficient film(represented by box 5) thereby forming a bonding layer between theoxygen deficient film and the SiO₂ film.

A specific example resulting from the process steps of FIG. 2a isdepicted in FIGS. 2b-2 d. Referring now to FIG. 2b, a metal stackcomprising Ti layer 11, Al/Cu layer 12 and Ti layer 13 has been formedon a supporting substrate 10 (supporting layer 10 represents anymaterial used in a fabrication process that the metal stack can beformed upon). Ti layer 13 is then cleaned by a method such as the onedescribed for FIG. 2a.

Referring now to FIG. 2c, an SiO_(x) layer 21 is formed over the cleanedsurface of Ti layer 13 by the plasma dissociation as described for FIG.2a. During this dissociation, not only is SiO_(x) layer 21 formed overthe cleaned surface of Ti layer 13, but Ti layer 13 is oxidized to formTiO₂ layer 20 that adheres Ti layer 13 to SiO_(x) layer 21.

Referring now to FIG. 2d, SiO₂ layer 22 is formed on SiO_(x) layer 21 bymethods known to those skilled in the art.

A third embodiment is a combination of the first two embodiments andreferring now to FIG. 3a, the general processing flow is outlined. Firstthe surface of a metal is cleaned by such methods as subjecting themetal to an argon plasma as represented by box 1. When subjecting themetal to argon plasma, the desired result is accomplished by aperforming a sputter clean at a pressure of approximately 30 mTorr, atan energy of approximately 200 W RF power, at an argon flow rate ofapproximately 50 sccm and at a time period of approximately 10 sec. Evenbetter results are obtained when employing a magnetic field ofapproximately 60 Gauss during the sputter clean. However, the range foreach of the parameters can vary. For example, the sputter clean can beperformed at a pressure range of 10-50 mTorr, at an energy range of100-500 W RF power, at an argon flow of 20-70 sccm and for a time periodof 5-50 sec.

Next, the metal surface is converted to nitride (as represented by box2) by such methods as subjecting the cleaned metal surface to plasmanitridation comprising N₂+NH₃ plasma. When subjecting the metal surfaceto plasma nitridation the metal surface is placed in an N₂/NH₃ ambientfor approximately 15 sec, at a pressure of approximately 4.5 Torr, at atemperature of approximately 360° C. and at an energy of approximately350 W RF power. It is preferred that the N₂:NH₃ ratio is 10:1, howeverit is sufficient if the ratio range is form 2:1 to 50:1.

Next, an oxygen deficient film is formed on the metal nitride asrepresented in box 6. For example, the oxygen deficient film comprisesSiO_(x) that is formed by the plasma dissociation of TEOS (where xvaries from 1-2).

And finally a SiO₂ film is formed over the oxygen deficient film(represented by box 7) thereby forming a bonding layer between theoxygen deficient film and the SiO₂ film.

A specific example resulting from the process steps of FIG. 3a isdepicted in FIGS. 3b-3 e. Referring now to FIG. 3b, a metal stackcomprising Ti layer 11, Al/Cu layer 12 and Ti layer 13 has been formedon a supporting substrate 10 (supporting layer 10 represents anymaterial used in a fabrication process that the metal stack can beformed upon). Ti layer 13 is then cleaned by a method such as the onedescribed for FIG. 3a.

Referring now to FIG. 3c, the cleaned surface of Ti layer 13 is exposedto plasma nitridation by a method such as the one described for FIG. 3a.The resulting nitridation of the surface of Ti layer 13 forms TiN layer14.

Referring now to FIG. 3d, an SiO_(x) layer 31 is formed over Ti layer 13by the plasma dissociation as described for FIG. 3a. During thisdissociation, not only is the SiO_(x) layer 31 formed over Ti layer 13,but TiN layer 14 is converted to an interfacial layer 30 that comprisesTi/O/N layer 30 and adheres Ti layer 13 to SiO_(x) layer 31.

Referring now to FIG. 3e, a second SiO₂ layer 32 is formed on the firstSiO₂ layer 32 by methods known to those skilled in the art.

It is to be understood that although the present invention has beendescribed with reference to several embodiments, various modificationsor other combinations of these embodiments, may be made to the structureand process steps presented herein without departing from the inventionas recited in the several claims appended hereto.

What is claimed is:
 1. A method for forming a structure having a silicondioxide film bonded to a metal film comprising: bonding a metal nitridefilm to said metal film; bonding an oxygen deficient film consisting ofsilicon oxide to said metal nitride film; and bonding said silicondioxide film to said oxygen deficient film.
 2. A method for forming astructure having a silicon dioxide film bonded to a metal filmcomprising: bonding a metal oxide film to said metal film; bonding anoxygen deficient film consisting of silicon oxide to said metal oxidefilm; and bonding said silicon dioxide film to said oxygen deficientfilm.
 3. A method for forming a structure having a silicon dioxide filmbonded to a metal film comprising: bonding a metal/oxide/nitride film tosaid metal film; bonding an oxygen deficient film consisting of siliconoxide to said metal/oxide/nitride film; and bonding said silicon dioxidefilm to said oxygen deficient film.